Dissertation

|3.4 Outlook, Exploratory Investigations and Perspectives|
combines the concept of ip-bridges with the binuclear palladium catalyst, so that intramolecular
photocatalysts can be generated which carry two {Ru(̂LL) 3 } 2+ -type chromophores. Thus,
purposeful functionalization of the imidazole nitrogens with aryl bridge/spacer was attempted
to yield a suitable 1-substituted, 3-bridged bis-1H-imidazo[4,5-f][1,10]phenanthrolinium salt (see
figure 118).
Br
Br
N
H
N
Br
N
N
N
N
Br
Br
N
N
N
N
method L2
N
N
method L3
N
N
N
N
ip eip edip
Figure 118: Two-step synthesis of 1,1’-[(2,3,5,6-tetramethylbenzene-1,4-diyl)dimethanediyl]bis(3-
ethyl-1H-imidazo[4,5-f][1,10]phenanthrolinium) dibromide (edip).
The selective introduction of an ethyl moiety into the 1-position of ip was achieved according
to method L2 via the substitution reaction with ethyl bromide to yield 1-ethyl-1H-imidazo[4,5-
f][1,10]phenanthroline (eip) in good yields.
The 1 H-NMR-spectrum showed similar peak patterns as ip, with the expected asymmetry of the
ip-backbone, the singlet signal of the 2-proton (δ eip
(2)
= 7.96 ppm) as well as the aliphatic signals
of the ethyl group with the correct integral values and similar chemical shifts, as observed in
the case of bip (δ eip
(CH 2 ) = 4.611 ppm (q, 2H, 3 J = 7.2 Hz) and δ eip
(CH 3 ) = 1.655 ppm (t, 3H, 3 J = 7.2 Hz)).
Assignment of the 13 C-NMR-signals reveals chemical shifts, which are consistent with previous
data (e.g. δ eip
bip
(C2)
= 141.98 ppm, compare δ(C2) = 143.54).
After its successful synthesis, eip was used as starting material in the reaction with 4,6-dibromomethyldurene
according to method L3. This transformation gave 1,1’-[(2,3,5,6-tetramethylbenzene-1,4-diyl)dimethanediyl]bis(3-ethyl-1H-imidazo[4,5-f][1,10]phenanthrolinium)
dibromide
(edip) as a white precipitate in 50% yield. The formation of the desired compound was confirmed
via 1 H- and 13 C-NMR spectroscopy and mass spectrometry. In the 1 H-NMR spectrum of
the asymmetric compound all eleven (seven aromatic and four aliphatic) signals were found
(see figure 119 on page 166). Of interest is the characteristic singlet of the proton in 2-
position (δ edip
(2)
= 9.04 ppm) and the singlet of the durene methyl groups (δ edip
(CH 3 -Ar)
= 2.25 ppm).
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